The present invention relates to lithography that may be used to produce integrated circuits and microdevices. More specifically, the present invention relates to a process of using an improved mold or microreplication surface in a process that creates patterns with ultra fine features in a thin film carried on a surface of a substrate.
In the fabrication of semiconductor integrated electrical circuits, optical, magnetic, mechanical circuits and microdevices, and the like, one of the key processing methods is lithography and especially photolithography. Lithography can be used, along with its traditional resist imaging in the formation of printing plates and resist images, to create a pattern in a thin film carried on a substrate so that, in subsequent process steps, the pattern can be replicated in the substrate or in another material which is added onto the substrate. The thin film which accepts a pattern or image during the lithographic process is often referred to as resist. The resist may be either a positive resist or a negative resist, depending on its operation of formation. For example, a positive photoresist becomes more soluble in a solvent irradiated and a negative resist becomes more insoluble where irradiated. A typical lithographic process for integrated circuit fabrication involves irradiating a photoresist composition or film with a beam of radiation particles, including light, energetic particles (which may be electrons), photons, or ions, by either passing a flood beam through a mask or scanning a focused beam. The radiation or particle beam changes the chemical structure of the exposed area of the film, so that when washed or immersed in a developer, either the exposed area or the unexposed area of the resist will be removed to recreate the patterns on its obverse of the mask or the scanning. The lithography resolution is limited by the wavelength of the particles and the resolution of the beam, the particle scattering in the resist and the substrate, and the properties of the resist.
There is an ongoing need in art of lithography to produce progressively smaller pattern sizes while maintaining cost efficiency in the process. There is a great need to develop low-cost technologies for mass producing sub-50 nm structures since such a technology could have an enormous impact in many areas of engineering and science. Not only will the future of semiconductor integrated circuits be affected, but also the commercialization of many innovative electrical, optical, magnetic, mechanical microdevices that are far superior to current devices will rely on the possibility of such technology. Additionally optical materials, including reflective coatings and reflective sheeting (as may be used for security purposes or for signage) can use microreplication techniques according to lithographic technology.
Numerous technologies have been developed to service these needs, but they all suffer serious drawbacks and none of them can mass produce sub-50 nanometer features at a low cost. Electron beam lithography has demonstrated 10 nm lithography resolution. A. N. Broers, J. M.Harper, and W. W. Molzen, Appl. Phys. Lett. 33, 392 (1978) and P. B. Fischer and S. Y. Chou, Appl. Phys. Lett. 62, 2989 (1993). However, using these technologies for mass production of sub-50 nm structures seems economically impractical due to inherent low throughput in a serial processing tool. X-ray lithography, which can have a high throughput, has demonstrated 50 nm lithography resolution. K. Early, M. L. Schattenburg, and H. I. Smith, Microelectronic Engineering 11, 317 (1990). But X-ray lithography tools are expensive and their ability for mass producing sub-50 nm structures is yet to be commercially demonstrated. Lithography based on scanning probes has produced sub-10 nm structures in a very thin layer of materials. However, the practicality of such lithography in a manufacturing tool is hard to judge at this point.
Imprint technology using compressive molding of thermoplastic polymers is a low cost mass manufacturing technology and has been around for several decades. Features with sizes greater than 1 micrometer have been routinely imprinted in plastics. Compact disks which are based on imprinting of polycarbonate are one example of the commercial use of this technology. Other examples are imprinted polymethyl methacrylate (PMMA) structures with a feature size on the order to 10 micrometers for making micromechanical parts. H. Harmening, W. Bacher, P. Bley, A. El-Kholi, H. Kalb, B. Kowanz, W. Menz, A. Michel, and J. Mohr, Proceedings IEEE Micro Electro Mechanical Systems, 202 (1992). Molded polyester micromechanical parts with feature dimensions of several tens of microns have also been used. H. Li and S. D. Senturia, Proceedings of 1992 13th IEEE/CHMT International Electronic Manufacturing Technology Symposium, 145 (1992).